I have a longjohn because it was cheaper and I liked the thought of having my shoulders free of friction or resistance to movement. Having said that the research clearly shows a full suit is more buoyant and therefore faster, perhaps on the order of 2 seconds per 100 meters, a significant time difference for the Olympic and longer swims.

Think about it. All the pros wear full suits.

BUT, the full has to fit properly, so you need to find someone that knows what they're doing to get you the right fit.

BTW, Anton, appreciate your helpful responses to these questions.